1. Field of the Invention
The present invention relates to a piston type compressor, having a gas flow structure, with a fluid port and a valve capable of flexural deformation for opening and closing the fluid port, for passing a gas through the fluid port, by pushing the valve open by the operation of each piston in the cylinder bore.
2. Description of the Related Art
When a gas is sucked from a suction chamber into a cylinder bore in a piston type compressor, the facility or ease of the inflow of the gas greatly affects the volumetric efficiency.
A suction port disclosed in Japanese Unexamined Patent Publication (Kokai) No. 57-97974 is circular and a suction port disclosed in Japanese Unexamined Patent Publication (Kokai) No. 2000-54961 is somewhat rounded and substantially triangular. A gas passing through the suction port from a suction chamber towards a cylinder bore exclusively flows in a direction perpendicular to a contour line of the suction port, as viewed from the reciprocating direction of a piston, (the circular port in Japanese Unexamined Patent-Publication (Kokai) No. 57-97974 and the rounded triangular port in No. 2000-54961) and enters the cylinder bore. The opening gap of the suction valve relative to the valve plate becomes progressively greater towards the distal end of the suction valve. It is therefore effective to let the gas passing through the suction port flow in the longitudinal direction of the suction valve from its distal end side in order to improve the facility of the inflow of the gas. The gas passing through the suction port exclusively flows in the direction perpendicular to the contour line that forms the hole of the suction port. Therefore, it can be said, in connection with the contour line of the suction port, that the greater the length of the contour line on the distal end side of the suction valve, the easier it becomes for the gas to flow towards the distal end side of the suction valve. The suction port described in Japanese Unexamined Patent Publication (Kokai) No. 2000-54961 is superior to the circular suction port described in Japanese Unexamined Patent Publication (Kokai) No. 57-97974 because the gas passing through the suction port can flow more easily from the distal end side of the suction valve in its longitudinal direction in the former than in the latter. Therefore, the ease of the inflow of the gas is higher in the suction port of Japanese Unexamined Patent Publication (Kokai) No. 2000-54961 than in the circular suction port of the Japanese Unexamined Patent Publication (Kokai) No. 57-97974.
The cross section of the suction port described in Japanese Unexamined Patent Publication (Kokai) No. 2000-54961 is formed in such a shape that the center of gravity of the area of the suction port is shifted toward the side of the proximal end of the suction valve. In this shape of the suction port, in the case where the suction port is divided into two sections so that the length of one section in the longitudinal direction of the suction valve is the same as that of another section, the length of a portion of a contour line of the suction port located on the side of the proximal end of the suction valve is greater than that of a portion of the contour line of the suction port located on the side of the distal end of the suction valve. This length relationship between the portions of the contour line cannot be said to optimum for the easy inflow of the gas toward the distal end side of the suction valve.
The object of the present invention is to provide a piston type compressor which can improve the ease of the inflow of the gas through a fluid port such as a suction port or a discharge port.
To accomplish this object, the present invention provides a piston type compressor comprising a housing having cylinder bores, and fluid ports in communication with the cylinder bores, pistons reciprocatingly arranged in the cylinder bores, a drive shaft rotatably supported by the housing, a transmission mechanism operatively coupled to the drive shaft and the pistons for converting rotation of the drive shaft into reciprocal movement of the pistons, and valves to open and close the fluid ports. The valve has a longitudinal direction, a proximal end and a distal end at the opposite end to the proximal end. A middle line is provided which passes through a middle point of a maximum length of the fluid port in the longitudinal direction of the valve, extends transversely with respect to the fluid port and perpendicularly crosses a reference line extending in the longitudinal direction of the valve. The middle line divides the fluid port into a first section positioned on the side of the proximal end portion of the valve and a second section positioned on the side of the distal end of the valve. An area of the second section is greater than an area of the first section.
The construction in which the area of the second section is greater than the area of the first section makes it easier for the gas passing through the fluid port to flow from the distal end side of the valve.
Preferably, a width increasing region is disposed in which the width of the fluid port in a direction of the middle line becomes gradually greater from the proximal end side to the distal end side of the valve in the longitudinal direction of the valve, and the length of the width increasing region in the direction of the reference line occupies a major part of the maximum length of the fluid port in the direction of the reference line.
The existence of the width increasing region makes it easier for the gas passing through the fluid port to flow towards the distal end side of the valve.
Preferably, a maximum width of the fluid port in the direction of the middle line exists in the second section and is greater than the maximum length of the fluid port in the direction of the reference line.
The construction in which the maximum length of the fluid port in the direction of the reference line is smaller than the maximum width of the fluid port in the direction of the middle line and the maximum width of the fluid port in the direction of the middle line exists on the side of the second section is convenient for increasing the length of the contour line of the fluid port on the distal end side of the valve.
Preferably, the fluid port has a contour line comprising a proximal end line positioned on the side of the proximal end of the valve, a distal end line positioned on the side of the distal end of the valve and a pair of right and left side lines, and the distal end line is longer than the proximal end line.
The construction wherein the length of the distal end line is greater than that of the proximal end line makes it easier for the gas passing through the fluid port to flow towards the distal end side of the valve.
Preferably, the distal end line comprises a convex curve protruding from the proximal end side to the distal end side of the valve.
The construction in which the distal end line comprises a convex curve is advantageous in bringing the distal end line closer to the circle of the circumferential surface of the cylinder bore. The closer the distal end line is to the circle of the circumferential surface of cylinder bore, the greater is the opened gap between the distal end line and the valve in the open condition.
Preferably, the contour line of the fluid port includes a pair of first connection lines connecting the proximal end line to the pair of side lines and a pair of second connection lines connecting the distal end line to the pair of side lines, the pair of first connection lines being smoothly connected to the proximal end line and the pair of said side lines, the pair of second connection lines being smoothly connected to the distal end line and the pair of side lines.
Preferably, the contour line of the suction port is an annular line with no corner. The construction wherein the contour line of the fluid port is an annular line with no corner is advantageous for preventing backflow of the gas in the fluid port.
Preferably, the contour line of the suction port is an annular convex line with no corner.
Preferably, the reference line extends substantially along the radial line of the circle of the circumferential surface of the cylinder bore.
The construction wherein the reference line extends substantially along the radial line of the circle of the circumferential surface of the cylinder bore is advantageous for bringing the contour line of the fluid port on the distal end side of the valve closer to the circle of the circumferential surface of the cylinder bore.